1. Field of the Invention
The present invention relates to an article production system in which automated process operations performed by a plurality of automatic processing machines and manual process operations performed by a plurality of workers are mixed together, and, more particularly, to a production system including shuttles that convey workpieces while reciprocating at high speed.
2. Description of the Related Art
A conventional production system that manufactures vehicle engines or the like is shown in FIG. 1. In this production system, a plurality of automatic processing machines 2 that apply various process steps, such as machining, attachment of parts, screw loosening, and screw tightening, onto workpieces W, such as engine cylinder blocks or engine cylinder heads, are arranged along a conveying line 1 that conveys workpieces W. Manual work areas 3 in which workers M can perform various process operations by manual work are located between the automatic processing machines 2.
In this production system, since the automated process steps and the manual process steps are performed in series with each other, the absence of any one of these process steps causes a stoppage in the flow of the whole of the system, and, since the system has an arrangement structure in which the manual work area 3 (i.e., the manual process step) is located between the automatic processing machines 2, one worker M has difficulty in performing a plurality of manual process operations across the automatic processing machine 2. Therefore, a conventional problem resides in the fact that it is difficult to efficiently station the workers M, for example, when a production adjustment is required to be carried out in response to a demand drop in the market.
Additionally, in one conveying line, workpieces W being conveyed on the upstream side of the flow line must be held until all process operations to be performed by the automatic processing machine 2 are completed if the automatic processing machine 2 has a plurality of processing functions. Additionally, when the automatic processing machine 2 is replaced in accordance with a change in specifications of the workpiece W or a change in the machine model, all conveying lines must be stopped. Therefore, another conventional problem resides in the fact that it is not easy to increase the amount of production in response to a demand rise in the market, and that it is not easy to change the automatic processing machine 2 or add a new machine so as to be suited to workpieces W.
On the other hand, a production system capable of increasing and decreasing the number of pieces of equipment in accordance with an increase and decrease in the amount of production is known. This production system includes one conveying line having shuttles that convey workpieces, an automatic processing machine that is disposed on one side of the conveying line and that automatically performs a plurality of process operations, and a plurality of manual work stands that are disposed on the opposite side of the conveying line and in which workers perform various process operations by hand (see Japanese Unexamined Patent Publication No. 2001-18869, for example).
However, in this production system, the manual work stands are disposed adjacent to each other on the same side. Therefore, there is a fear that a worker will handle a workpiece conveyed to a manual work stand by a shuttle without following a correct procedure (for example, a process step may be performed prior to the proper time, or a worker in charge of a manual work area will perform a series of process operations in improper order). Additionally, workpieces are all transferred by shuttles between the automatic processing machine and the manual work stand and between the two manual work stands. Therefore, it is difficult to, for example, smoothly convey a workpiece, which has undergone faulty processing, to a manual work stand located on the upstream side in order to apply an alteration to this workpiece, and hence it is impossible to smoothly apply all of the process steps to the workpiece.